1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to an LED backlight driving circuit and LED backlight driving method.
2. The Related Arts
Liquid crystal display (LCD) has a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and is thus widely used. Most of the LCDs that are currently available in the market are backlighting LCDs, which comprise a liquid crystal panel and a backlight module. The operation principle of the liquid crystal panel is that liquid crystal molecules are interposed between two parallel glass substrates and a plurality of vertical and horizontal fine electrical wires is arranged between the two glass substrates, whereby the liquid crystal molecules are controlled to change direction by application of electricity in order to refract light emitting from the backlight module for generating images. Since the liquid crystal panel itself does not emit light, light must be provided by the backlight module in order to normally display images. Thus, the backlight module is one of the key components of an LCD. The backlight module can be classified in two types, namely side-edge backlight module and direct backlight module, according to the position where light gets incident. The direct backlight module arranges a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED), at the back side of the liquid crystal panel to form a planar light source that directly provides lighting to the liquid crystal panel. The side-edge backlight module arranges an LED light bar of a backlight source at an edge of a backplane that is located rearward of one side of the liquid crystal panel. The LED light bar emits light that enters a light guide plate (LGP) through a light incident face of the light guide plate and is projected out through a light emergence face of the light guide plate, after being reflected and diffused, to thereby transmit through an optic film assembly to form a planar light source for the liquid crystal panel.
Referring to FIG. 1, a conventional method for driving LED light bar of back light source adopts an arrangement of serially connecting a dimming MOS transistor Q10 with an isolation MOS transistor Q20. This leads to an extremely high current I flowing through the isolation MOS transistor thereby inducing a large amount of heat, an excessively high temperature, and lowered circuit safety. To solve such a problem, a conventional solution uses an over-specification isolation MOS transistor (such as having better resistance against high temperature). This definitely increases the cost to some extents.